An optical fiber grating widely used for optical communication and fiber optic sensor devices is generally manufactured by the change of a refractive index of a fiber optic core which is generated by radiating strong ultraviolet rays on the optical fiber.
At this point, the optical fiber grating is classified as a short period optical fiber grating and a long period optical fiber grating according to the characteristic of the optical fiber, such as a refractive index modulation period or the like, and studied and used as a reflection and penetration filter or the like in relation to the wavelength based on the characteristic.
In addition, a fiber Bragg grating induces periodic changes of the refractive index of the optical core in the axial direction. The optical fiber grating has a characteristic of reflecting only the rays satisfying a Bragg condition and having a narrow line width (generally, 0.1 to 1 nm) around a Bragg wavelength and passing rays of the other wavelengths. If temperature of the fiber Bragg grating is changed or a stress is applied to the fiber Bragg grating, the Bragg wavelength also is changed. Accordingly, a variety of fiber-optic grating sensors for measuring temperature, strain, pressure or the like using the characteristic have been developed.
However, since the fiber-optic grating sensor requires an expensive reference fiber Bragg grating (FBG), it is expensive and has a complex structure. Accordingly, development of a measure for implementing a fiber-optic grating sensor of a low price and a simple structure is required.